1. Field of the Invention
The present invention generally relates to an apparatus and method for sampling a fluid over a period of time.
2. Description of the Related Art
Devices for periodically testing a gas to provide a time domain of chemical background are known. Such devices include, for example, multiple metal or glass tubes, each tube having a sorbent material. Generally, gas is drawn through one of these tubes using a commercial pump and the results are analyzed using a commercial thermal desorber and an analysis unit such as, for example, a gas chromatograph, mass spectrometer, or pulse flame photometer.
Currently, to obtain information in the time domain, i.e., sampling measurements over a period of time to determine changes in composition, it is necessary to use a cascade of tubes and a complex set of valves or a continual manual change of values or some other extensive and/or expensive technique.
For example, U.S. Pat. No. 6,321,609 B1 discloses a gas sampling system having a removable magazine that fits within a port of a trapping module and has a rotating carousel with multiple individual sample tubes. However, when multiple sample tubes are used, the sample must be exposed to a small amount of sorbent at any given time, and when multi-bed absorbent mixtures are used, non-symmetric exposure typically occurs. All of these occur without time domain data. What is needed is the ability to have target compounds exposed to and absorbed onto a series of absorbent materials and the ability to desorb the compounds so as to retrieve composition data of target compounds and/or compositions over a period of time.